The present invention relates to a sensor for sensing a pressure in a dirty and severe atmosphere, particularly, a combustion pressure of an automobile engine.
As combustion pressure sensors of this type, those using a piezoresistance effect of a silicon semiconductor substrate known, for example, from Japanese Patent Laidopen Nos. Hei 5-264390 and Hei 6-34475, have been already put in practical use. The combustion pressure sensor of this type has a configuration that a sensing portion composed of a silicon semiconductor substrate is separated from a dirty and severe combustion gas atmosphere at a high temperature, using a metal diaphragm. Specifically, a combustion pressure is converted into a force by means of the metal diaphragm, and is then transmitted to the silicon semiconductor substrate disposed at a relatively low temperature portion, at which the force is further converted into an electric signal.
The above-described prior art type pressure sensor is difficult to sense a combustion pressure in a state that the sensing portion is directly exposed to a dirty atmosphere in an automobile engine, which is raised at a high temperature and is rapidly varied in temperature, and is also brought in direct-contact with a combustion gas. In particular, the prior art pressure sensor has a disadvantage that there arises a significantly large sensing error due to a temperature effect exerted on the pressure sensor exposed to an environment raised at a high temperature and rapidly varied in temperature. Another problem is that the sensing portion exposed at a dirty environment at a high temperature is possibly broken for a short time, resulting in the degraded reliability. In addition, the prior art type pressure sensor is difficult to accurately sense abnormal combustion of an engine such as a knocking phenomenon because the sensing portion cannot be directly exposed to a combustion gas atmosphere. To be separated from the combustion gas atmosphere, the sensing portion must be manufactured into a large complex structure at a high cost. The prior art pressure sensor, having a large-sized sensing portion, is poor in mounting characteristic to an engine and is difficult to be mounted in each cylinder of the engine. Additionally, there has been not proposed yet an inexpensive signal processor circuit capable of sensing combustion pressures at a high accuracy when pressure sensors are individually mounted in all engine cylinders.